It might be better to wait to have kids until you are finished with
your post-doctoral studies (if this is possible). I say this because
If you wanted to take off time to raise your children, there is
money available from NIH in the form of reentry supplements. You
must have taken off at least two years and not have worked more
than 10 hours per week in the interim...but if you find a lab to
sponsor you in the reentry process, the supplement covers your
salary and requires that you are given a faculty position (you don't
need to repeat your post-doc).
Jack